A typical garage door generally has multiple door panel sections (hinged together) that roll upward on parallel side tracks to move from a closed, vertical position to an open, horizontal, overhead position. A torsion spring connected to a shaft line supplies the power to balance the door throughout the opening operation. The spring generally has constant power per inch of rotation of the spring and travel of the door. However, some doors have a top door panel section that is heavier than the other sections; for example, some doors have windows or other ornamental features only on the top door panel section. With such doors having a heavy top door panel section, the loss of weight per inch of travel during opening is not constant. Accordingly, conventional door opening systems do not balance the uneven weight distribution.
Typically, the installation of a “top-heavy” door falls into one of two categories. In the first alternative, a spring lifting force is slightly less than optimal at the beginning of the door opening path but is sufficient once the heavy top door panel section has been lifted onto the horizontal track. This arrangement may strain the door lift motor, leading to premature wear and failure. In a second scenario, there is sufficient lifting force at the beginning of the opening process, but then there is excess force once the heaviest top door panel section has been lifted. This excess force may strain the attachment components securing the door to the garage, thereby leading to loosening of the attachments over time.